The present invention relates to a pneumatic tire, more particularly to a tread structure suitable for all-season heavy duty tires.
All-season tires for the use in areas that receive moderate levels of snowfall, are usually provided with block-type tread patterns in order to provide good traction.
Such all-season tires are becoming popular even in heavy duty vehicles, e.g. trucks, buses and the like because a level of traction can be obtained throughout the entire year and also because of the convenience of avoiding a tire changeover.
In general, a block-type tread pattern is made up of blocks arranged in a plurality of circumferential rows, for instance as disclosed in the Japanese patent application publication JP-A-2002-67624. Since the blocks are separated from each other by tread grooves, the rigidity thereof is relatively low. Thus, during running, the blocks in the ground contacting patch are liable to move against the road surface, causing uneven wear such as so-called heel-and-toe wear.
Incidentally, the heel-and-toe wear is a state of uneven wear of a block, namely, such a state that the toe-side edge and heel-side edge of a block are worn out more than the other portions of the block. Usually, wear starts from the corners of the block and expands into heel-and-toe wear. If the heel-and-toe wear is large, the wear of the entire block becomes rapid.
In general, on the other hand, the ground pressure of a heavy duty tire has a tendency to increase gradually from the tread shoulders to the tread center due to a round tread profile. Therefore, as the position of a block becomes closer to the tread center, the block suffers from a larger wear.